Unix is a computer operating system originally developed in 1969 by AT&T employees at Bell Labs. Today's Unix systems are split into various branches, developed over time by AT&T as well as various commercial vendors and non-profit organizations.
As of 2007, the owner of the trademark UNIX® is The Open Group, an industry standards consortium to define Unix standards and certificate Unix products. Only systems fully compliant with and certified to the Single UNIX Specification qualify as "UNIX®", while others are called "Unix-like". Unix and Unix-like OSs are widely used in servers, workstations, embedded systems and supercomputers.
During the late 1970s and early 1980s, Unix's influence in academic circles led to large-scale adoption of Unix (particularly of the BSD variant, originating from the University of California, Berkeley) by commercial startups such as Sun Microsystems. Today, in addition to certified Unix systems, Unix-like operating systems such as the open source Linux and BSD derivatives are commonly encountered.
There are a few main branches for the Unix and Unix-like operating systems in the development history of past decades. System V has been considered one of the major "flavors" of UNIX, so is the BSD based branches. Linux has also become a very popular OS with multiple code bases. In the table below, we listed the timeline of the main branches for the Unix and Unix-like computer operating systems.
| Date | OS Edition | Platform | Notes |
| 1969 | UNICS | DEC PDP-7 | The Unix story started by Ken Thompson, Dennis Ritchie and others in Bell Labs. |
| 1971 | Unix v1 | PDP-11/20 | The name Unix was firstly used. Assemble language based. |
| 1972 | Unix v2 | ||
| 1973 | Unix v3 | ||
| 1973 | Unix v4 | Unix was re-written in C language. | |
| 1974 | Unix v5 | ||
| 1975 | Unix v6 | This version was widely used outside the Bell Labs. BSD version (1.x) was derived from V6. | |
| 1978 | 1BSD | DEC PDP-11 | The first Unix BSD version, Berkeley Software Distribution. It was an add-on to Unix v6. |
| 1979 | Unix v7 | DEC VAX, etc. | |
| 1979 | 2BSD | DEC VAX | |
| 1980 | 3BSD | DEC VAX | |
| 1980 | 4BSD | DEC VAX | |
| 1981 | 4.1BSD | DEC VAX | Some Unix versions such as SunOS are based on this release. |
| 1981 | Unix System III | This release is based on the CB Unix 3. It is the first public release outside Bell Lab. | |
| 1982 | Unix System IV | Sun Microsystems joined AT&T to develop and implement this release. | |
| 1982 | SunOS 0.7 | Bundled with 68000-based Sun-1 system | UniSoft UNIX v7 |
| 1983 | Unix System V | The first supported release with broad implementations. Many companies licensed this release to develop their own commercial versions. | |
| 1983 | SunOS 1.0 | For Sun-1 and Sun-2 systems | Based on 4.1BSD and SunOS 0.7 |
| 1984 | Unix 4.2BSD | DEC VAX | University of California at Berkeley release. |
| 1984 | Unix SVR2 (System V release 2) | ||
| 1985 | Unix v8 | ||
| 1985 | SunOS 2.0 | Based on 4.2BSD and SunOS 1.2 | |
| 1986 | Unix v9 | ||
| 1986 | SunOS 3.0 | Based on 4.2BSD+, System V IPC and SunOS 2.0 | |
| 1986 | HP-UX 1.0 | Based on Unix System V | |
| 1986 | Unix 4.3BSD | Started to separate OS from a specific machine such as VAX. | BSD license developed for free re-distribution. |
| 1987 | Unix SVR3 (System V release 3) | ||
| 1988 | SunOS 4.0 | Last release under the SunOS name; The name “Solaris” was back-filed from SunOS 4.1.1. | |
| 1988 | HP-UX 2.0 | ||
| 1988 | HP-UX 3.0 | ||
| 1989 | Unix v10 | ||
| 1989 | HP-UX 6.0 | HP 300 series | 4.3BSD socket was used. |
| 1989 | Unix SVR4 (System V release 4) | ||
| 1990 | HP-UX 7.0 | For 300/400, 600/700 (in 7.03) /800 HP systems. | Unix SVR4 code base was absorbed. |
| 1991 | HP-UX 8.0 | For 300/400, 600/700/800 HP systems. | |
| 1991 | Linux 0.01 | Open Source for Server, Workstation, Network Appliance, Embedded | Very first release of Linux under GNU GPL by Linus Torvalds. |
| 1992 | UnixWare 1 (Unix SVR4.2) | Released by Univel, a joint-owned venture of AT&T and Novell. | |
| 1992 | HP-UX 9.0 | For 300/400, 600/700/800 HP systems. | |
| 1992 | Solaris 2.0 (or SunOS 5.0) | sun4c architecture | First official release under the name Solaris. It is based on the Unix SVR4. |
| 1993 | Unix 4.4BSD and 4.4BSD Lite | Server and Desktops | The lawsuit between AT&T and Berkeley was settled largely in Berkeley's favor. The 4.4BSDLite has no AT&T code. Many Unix like OSs were forked from this version. |
| 1993 | FreeBSD 1.0 | Open Source for Server, Workstation, Network Appliance, Embedded | A branch through the 386BSD and 4.4BSD operating systems. |
| 1994 | FreeBSD 2.0 | Open Source for Server, Workstation, Network Appliance, Embedded | |
| 1994 | Linux 1.0 | Open Source for Server, Workstation, Network Appliance, Embedded | |
| 1994 | NetBSD 1.0 | Open Source for Server, Workstation, Network Appliance, Embedded | Based on BSD4.3 and 386BSD. |
| 1994 | UnixWare 2 (or Unix SVR4.2MP) | AT&T transferred its rights in Unival to Novell, who then owned the Unix trademark and UnixWare copyrights. | |
| 1995 | UnixWare 2.1 | Novell transferred the UNIX trademark to X/Open (now The Open Group) and the source code copyrights to SCO. This is the first release by SCO. | |
| 1995 | HP-UX 10.0 | For 700/800 HP systems. | |
| 1995 | OpenBSD 1.0 | Open Source for Server, Workstation, Network Appliance, Embedded | Forked from 4.4BSD Lite and NetBSD 1.0. |
| 1996 | OpenBSD 2.0 | ||
| 1996 | Linux 2.0 | ||
| 1996 | Linux 2.1.0 | ||
| 1997 | HP-UX 11.0 | For 700/800 HP systems. | First release to support 64-bit addressing |
| 1998 | UnixWare 7 (or Unix SVR5.0) | A "merge" of UnixWare 2 and OpenServer. | |
| 1998 | Solaris 7 (or SunOS 5.7) | SPARC and x86 | The first 64-bit UltraSPARC release. |
| 1998 | FreeBSD 3.0 | ||
| 1999 | Linux 2.2.0 | ||
| 1999 | Linux 2.3.0 | ||
| 2000 | Solaris 8 (or SunOS 5.8) | SPARC and x86 | |
| 2000 | HP-UX 11.11 (or 11i) | ||
| 2000 | FreeBSD 4.0 | ||
| 2001 | OpenUnix 8 (Or UnixWare 7.1.2) | A short lived name for UnixWare. | |
| 2001 | OpenBSD 3.0 | ||
| 2001 | Linux 2.4.0 | ||
| 2001 | Linux 2.5.0 | ||
| 2002 | SCO UnixWare 7.1.3 | The Open Unix name changed back to UnixWare. It is UNIX 95 standard compliant. | |
| 2002 | Solaris 9 (or SunOS 5.9) | SPARC and x86 | |
| 2003 | HP-UX 11.23 (or 11i v2) | For Itanium-based systems. | |
| 2003 | Linux 2.6.0 | ||
| 2003 | FreeBSD 5.0 | ||
| 2004 | NetBSD 2.0 | ||
| 2005 | Solaris 10 (or SunOS 5.10) | SPARC and x86 | |
| 2005 | SCO UnixWare 7.1.4 | Latest release. | |
| 2005 | Free BSD 6.0 | ||
| 2006 | NetBSD 3.0 | Open Source for Server, Workstation, Network Appliance, Embedded | The last version is NetBSD3.1 |
| 2006 | OpenBSD 4.0 | ||
| 2007 | Free BSD 7 | Open Source for Server, Workstation, Network Appliance, Embedded | The latest release. |
| 2007 | HP-UX 11.31 (or 11i v3) | For both PA-RISC and IA-64. | |
| 2007 | OpenBSD 4.1 | Open Source for Server, Workstation, Network Appliance, Embedded | The latest version. |
| 2007 | Linux 2.6.23.x | Open Source for Server, Workstation, Network Appliance, Embedded and Supercomputers | The Latest release. |